727 research outputs found
Use of inedible wheat residues from the KSC-CELSS breadboard facility for production of fungal cellulase
Cellulose and xylan (a hemicellulose) comprise 50 percent of inedible wheat residue (which is 60 percent of total wheat biomass) produced in the Kennedy Space Center Closed Ecological Life Support System (CELSS) Breadboard Biomass Production Chamber (BPC). These polysaccharides can be converted by enzymatic hydrolysis into useful monosaccharides, thus maximizing the use of BPC volume and energy, and minimizing waste material to be treated. The evaluation of CELSS-derived wheat residues for production for cellulase enzyme complex by Trichoderma reesei and supplemental beta-glucosidase by Aspergillus phoenicis is in progress. Results to date are given
System development and early biological tests in NASA's biomass production chamber
The Biomass Production Chamber at Kennedy Space Center was constructed to conduct large scale plant growth studies for NASA's CELSS program. Over the past four years, physical systems and computer control software have been continually upgraded and the degree of atmospheric leakage from the chamber has decreased from about 40 to 5 percent of the total volume per day. Early tests conducted with a limited degree of closure showed that total crop (wheat) growth from the best trays was within 80 percent of reported optimal yields for similar light levels. Yields from subsequent tests under more tightly closed conditions have not been as good--up to only 65 percent of optimal yields. Yields appear to have decreased with increasing closure, yet potential problems exist in cultural techniques and further studies are warranted. With the ability to tightly seal the chamber, quantitative data were gathered on CO2 and water exchange rates. Results showed that stand photosynthesis and transpiration reached a peak near 25 days after planting, soon after full vegetative ground cover was established. In the final phase of testing when atmospheric closure was the highest, ethylene gas levels in the chamber rose from about 10 to nearly 120 ppb. Evidence suggests that the ethylene originated from the wheat plants themselves and may have caused an epinastic rolling of the leaves, but no apparent detrimental effects on whole plant function
DMRG Study of Critical Behavior of the Spin-1/2 Alternating Heisenberg Chain
We investigate the critical behavior of the S=1/2 alternating Heisenberg
chain using the density matrix renormalization group (DMRG). The ground-state
energy per spin and singlet-triplet energy gap are determined for a range of
alternations. Our results for the approach of the ground-state energy to the
uniform chain limit are well described by a power law with exponent p=1.45. The
singlet-triplet gap is also well described by a power law, with a critical
exponent of p=0.73, half of the ground-state energy exponent. The
renormalization group predictions of power laws with logarithmic corrections
can also accurately describe our data provided that a surprisingly large scale
parameter is present in the logarithm.Comment: 6 pages, 4 eps-figure
Métodos de observação e análise para identificação das estruturas afiliativas de grupos de crianças em meio pré-escolar
Os modelos etológicos em desenvolvimento social sublinham que os grupos naturais proporcionam uma variedade de contextos sociais que influenciam de forma diferencial o crescimento e desenvolvimento individual. Contudo, os estudos comportamentais de primatas humanos e não-humanos têm sobretudo incidido nas relações de agressividade e estruturas de dominância. A investigação da organização do comportamento afiliativo tem sido impedida devido à falta de modelos e métodos para o estudo das estruturas sociais coesivas. As análises de agrupamento e redes sociais dos padrões de associação entre pares fornecem uma base alternativa para investigar a organização social de grupos infantis estáveis e para avaliar como é que os tipos afiliativos no interior do grupo podem influenciar o desenvolvimento individual. Os resultados do presente estudo contribuem directamente para a operacionalização de tais modelos descritivos das estruturas coesivas dos grupos de pares. A discussão dos resultados centra-se na forma como a inserção da criança na estrutura afiliativa do grupo de pares constrange o seu comportamento social e proporciona experiências específicas que servem como contextos para a construção de relações interpessoais mais íntimas
Quantum dots in magnetic fields: thermal response of broken symmetry phases
We investigate the thermal properties of circular semiconductor quantum dots
in high magnetic fields using finite temperature Hartree-Fock techniques. We
demonstrate that for a given magnetic field strength quantum dots undergo
various shape phase transitions as a function of temperature, and we outline
possible observable consequences.Comment: In Press, Phys. Rev. B (2001
The Role of Electron Captures in Chandrasekhar Mass Models for Type Ia Supernovae
The Chandrasekhar mass model for Type Ia Supernovae (SNe Ia) has received
increasing support from recent comparisons of observations with light curve
predictions and modeling of synthetic spectra. It explains SN Ia events via
thermonuclear explosions of accreting white dwarfs in binary stellar systems,
being caused by central carbon ignition when the white dwarf approaches the
Chandrasekhar mass. As the electron gas in white dwarfs is degenerate,
characterized by high Fermi energies for the high density regions in the
center, electron capture on intermediate mass and Fe-group nuclei plays an
important role in explosive burning. Electron capture affects the central
electron fraction Y_e, which determines the composition of the ejecta from such
explosions. Up to the present, astrophysical tabulations based on shell model
matrix elements were only available for light nuclei in the sd-shell. Recently
new Shell Model Monte Carlo (SMMC) and large-scale shell model diagonalization
calculations have also been performed for pf-shell nuclei. These lead in
general to a reduction of electron capture rates in comparison with previous,
more phenomenological, approaches. Making use of these new shell model based
rates, we present the first results for the composition of Fe-group nuclei
produced in the central regions of SNe Ia and possible changes in the
constraints on model parameters like ignition densities and burning front
speeds.Comment: 26 pages, 8 figures, submitted to Ap
Shape Coexistence and the Effective Nucleon-Nucleon Interaction
The phenomenon of shape coexistence is discussed within the self-consistent
Hartree-Fock method and the nuclear shell model. The occurrence of the
coexisting configurations with different intrinsic shapes is traced back to the
properties of the effective Hamiltonian.Comment: 40 pages (16 text, 24 figures). The file may also be retrieved at
http://csep2.phy.ornl.gov/theory_group/people/dean/shape_coex/shapes.htm
Captive breeding of Margaritifera auricularia (Spengler, 1793) and its conservation importance
Margaritifera auricularia is one of the most endangered freshwater mussels (Bivalvia, Unionida) in the world. Since 2013, the abundance of this species in the Ebro River basin (Spain) has sharply declined, driving the species to the verge of regional extinction. Therefore, any management measures that might facilitate the recovery of this species would be essential for its conservation.
During 2014–2016, captive breeding of M. auricularia allowed the production of >106 juveniles, out of which 95% were released into the natural environment, and 5% were grown in the laboratory under controlled conditions. The aim of this experimental work was to establish the best culture conditions for the survival and growth of M. auricularia juveniles in the laboratory.
The experiment was divided into two phases: phase I, in which juveniles recently detached from fish gills were cultured in detritus boxes until they reached a shell length of 1 mm; and phase II, in which these specimens were transferred to larger aquaria to grow up to 3–4 mm.
The best experimental conditions for juvenile survival and growth corresponded to treatments in glass containers at a density of 0.2 ind. L−1, using river water, with added substrate and detritus, enriched with phytoplankton, and avoiding extra aeration. The highest survival and growth rates attained, respectively, values of c. 60% at 100 days and 2.56 mm in shell length at 30–32 weeks.
This is the first study to report on the long‐term survival and growth of juvenile M. auricularia in the laboratory, providing essential information in order to implement future conservation measures addressed at reinforcing the natural populations of this highly threatened species in European water bodies.This project was funded by the Government of Aragón, Department of Rural Development and Sustainability and carried out by the Environmental Service Department of SARGA. Special thanks go to Manuel Alcántara, Miguel Ángel Muñoz, Ester Ginés, Carlos Catalá, and Juan Pablo de la Roche, who were involved in the project. The authors appreciate the work of the reviewer and editor who improved the quality of the manuscript. The Aragón's forest rangers are thanked for their assistance during fieldwork
Electron capture on iron group nuclei
We present Gamow-Teller strength distributions from shell model Monte Carlo
studies of fp-shell nuclei that may play an important role in the pre-collapse
evolution of supernovae. We then use these strength distributions to calculate
the electron-capture cross sections and rates in the zero-momentum transfer
limit. We also discuss the thermal behavior of the cross sections. We find
large differences in these cross sections and rates when compared to the naive
single-particle estimates. These differences need to be taken into account for
improved modeling of the early stages of type II supernova evolution
Many-body perturbation calculation of spherical nuclei with a separable monopole interaction: I. Finite nuclei
We present calculations of ground state properties of spherical, doubly
closed-shell nuclei from O to Pb employing the techniques of
many-body perturbation theory using a separable density dependent monopole
interaction. The model gives results in Hartree-Fock order which are of similar
quality to other effective density-dependent interactions. In addition, second
and third order perturbation corrections to the binding energy are calculated
and are found to contribute small, but non-negligible corrections beyond the
mean-field result. The perturbation series converges quickly, suggesting that
this method may be used to calculate fully correlated wavefunctions with only
second or third order perturbation theory. We discuss the quality of the
results and suggest possible methods of improvement.Comment: 20 Pages, 11 figure
- …